Answer:
You did not provide the whole question and there are many possible answers, but maybe this would help.
When you write a fraction, you just need to remember that you are writing the part over the whole.
The whole would be the number of students. In this case, the number of students is 8. The part it is asking for is the nmber of students who cleaned the tables.
So to write that in a fraction you write the part as the numerator and the whole as the denominator.